The present invention relates to lithography, and more particularly to photoresist methods and materials that accommodate short wavelength, high-energy, e.g., X-ray, lithography.
Manufacturing of integrated circuits has been greatly enabled by high-performance spin-on organic polymeric resists, but with some limitations. One limitation that must be overcome to perform efficient lithography at wavelengths below 100 nm is the unfavorable sensitivity-resolution tradeoff exhibited by conventional photoresists at these wavelengths. This is especially true in X-ray lithography where high throughput is currently limited by resists designed not for X-ray lithography but rather for 248 nm lithography. These resists operate at sensitivities that range from 120 to 200 mJ/cm2 under X-ray exposure, significantly slower than 20 to 40 mJ/cm2 generally desired for cost effective throughput.
To date, there has yet to be a resist that demonstrates sub-100 nm resolution while having X-ray sensitivity in the range of 20 to 40 mJ/cm2. In addition to sensitivity and resolution requirements, resists must maintain critical line-width control throughout the patterning process, including both imaging and subsequent transfer via plasma etch. Line-edge roughness on the order of 5-10 nm is a concern at 250 nm, but will render a lithographic process unworkable when critical dimensions fall below 100 nm.
From a resist viewpoint, all advanced energy sources can be categorized as one of two types. The first type provides highly absorbing energy such as 157 nm, EUV and low-kV electrons, that is fully absorbed by the top surface of the resist. The second type provides highly penetrating energy, such as X-ray and high-kV electrons, that is only partially absorbed by the resist layer, with much of the exposure energy passing into the underlying substrate. The low level of exposure energy that is absorbed by the resist layer leads to low resist sensitivities, which can in turn lead to reduced manufacturing throughput.
Thus, it is evident that there is a need for improved photoresist materials and methods for the use thereof in lithographic processes at wavelengths below about 100 nm. Indeed, there is a need for resist materials with increased energy absorption ability that can be widely used in X-ray and other high-penetration short-wave energy sources, and which exhibit improved line-width roughness. These improved materials and methods must further be suitable to meet commercial manufacturing throughput requirement. More specifically, there exists a need for photolithographic processes that can demonstrate sub-100 nm resolution while having X-ray sensitivity in a desired range of 20 to 40 mJ/cm2.